Conventional apparatus for coupling between two relatively moving elements, depending upon the application, include such elements as rotary transformers or flex leads. In the case of the rotary transformer in the conventional manner of use, a primary coil is wound upon one element of a relatively moving set, while a secondary coil is wound upon the other element. An air gap typically exists between the two coils necessitating the mutual or coupling flux that results in the transfer of a signal or power between the coils to cross the gap twice in a complete circuit between the coils. This arrangement not only contributes to a high magnetization current which develops a high loss factor in the primary current and low input impedance but permits a fluctuation in signal output at the secondary where variations in the gap are possible. In addition, such a device is susceptible to undesirably large forces or torques developed between the two coils and the elements upon which they are formed.
The flex lead which has use in a device for transmitting electrical signals between relatively moving elements of limited degrees of motion, avoids the difficulties of rotary transformers attributable to the less than ideal flux path found in rotary transformers, but has its own deficiencies which include a potentially more limited degree of motion permitted between the moving elements, flex lead creep resulting from thermal and aging factors, as well as a greater susceptibility to damage from mechanical shock.